Fossil energy has been the most important and indeed the overwhelmingly dominating energy source. While the exhaustiblility of the fossil energy has been gradually ignored as our memory of energy crisis, which peaked in the late 1970's, gradually faded away. However, the use of fossil energy also posses another imminent problem, i.e., the global warming effect. It has been reported that the use of fossil energy has contributed to an increase in the carbon dioxide content in the atmosphere of about 1 ppm per year. This also causes the concern of the so-called green house effect.
The use of inexhaustible solar energy has been a topic of great interest. A solar cell can convert solar energy into electrical energy in a safe, convenient, pollution-free, and, theoretically, very inexpensive manner. The majority of the cost in installing a solar cell system is in the capital cost. The acceptability of solar cells depends on whether we can reduce the manufacturing cost thereof, and prolong its service life. The latter not only is directly related to the overall cost of using a solar cell system, it also prevents the problem of causing another type of pollution resulting from waste disposal.
Because the energy output from a single solar cell is very limited, typically a plurality of solar cells are connected together via interconnects to form a solar cell module. A solar cell module, which can produce from tens to thousand watts of electrical power output, thus constitutes the basic unit of solar cell systems. A solar cell system can consist of tens or thousand of solar modules. Some commercial solar cell systems can produce tens to tens of millions or even billions of watts of power output.
In order to minimize the environmental effects, such as "sunshine", rain, humidity, hail, snow, dust, and day-night and seasonal temperature changes, the solar cell systems, which include the solar cell modules and the connecting interconnects, are typically encapsulated, and the solar cells are made from mono- or polycrystalline silicon materials to form C--Si solar cell modules. This protective requirement is even more stringent for middle and large scale direct and alternating power supplies, as well as in communications and satellite applications.
In the manufacturing of a C--Si solar cell, which typically comprises a silver pad, wafer, and an anti-reflection coating on a polished semiconductive crystalline silicon material, silicon nitride has been used to form the anti-reflecting layer via deposition procedure. The thickness of the anti-reflection layer is approximately 700 .ANG.. This thickness causes a near-dark-blue color to be exhibited on the crystalline silicon substrate, so as to facilitate effective absorption of light by the solar cell.
Silicon nitride has many advantages for use in making solar cells, most notably its excellent chemical and mechanical strengths. However, the chemical inertness of silicon nitride makes it relatively difficult to weld interconnects on the silicon nitride surface. Typically, a flux is required to be applied on the interconnects during the welding process to improve the weld strength. Unfortunately, the use of flux in welding interconnects to the silicon nitride surface also introduces another problem in that the flux can cause oxidation or corrosion in the solar cell and/or the electrodes. This can adversely affect the energy conversion efficiency as well as the reliability and stability of the solar cells. Thus, the issue as to how to best encapsulate the solar module so as to provide the intended protection against environmental factors while improving its service life and reliability and stability, remains an important subject.
The idea of using adhesives in making solar cell modules has been largely ruled out because, after the adhesive is cured and hardened, it can be easily cracked under thermal or mechanical stress, thus rendering the application of adhesive useless. As a result, research and development efforts have focused on other aspects of solar cell manufacturing. For example, U.S. Pat. No. 4,173,820 disclosed a method for forming flexible solar array strips. U.S. Pat. No. 5,006,179 disclosed an improved solar cell interconnect with increased life expectancy when subjected to extended periods of severe thermal cycling. U.S. Pat. No. 5,074,920 disclosed a photovaltic cell with improved thermal stability by providing a silver thick film which are electrically interconnected to the photovaltic using a tin/silver solder paste to solder the silver thick film. The use of tin/silver solder paste could cause oxidation and/or corrosion problems.